Applicant's U.S. Pat. No. 9,913,371, incorporated herein by reference, describes how to print circuit components, such as diodes, in an array of tiny dots. Each diode may have a width between 10-200 microns. The positions of the dots may be accurately determined by screen printing, flexography, or other printing technique. Each dot contains a few identical diodes, and the number of diodes in a single dot is random due to the diodes being infused in a liquid ink and printed. For example, there may be an average of five diodes in a single dot.
The diodes are shaped to generally orient themselves in the desired direction (e.g., anode facing up) on an array of conductive areas on a substrate surface as the diodes settle on the substrate surface prior to curing the ink. For example, the diodes may have a relatively tall, narrow anode contact on top and a wide heavy cathode contact on the bottom so that the diodes settle on the substrate surface with the cathode facing the conductive area on the substrate. After curing the ink, the cathode electrically contacts the associated conductive area.
After the diodes are printed and cured, a thin dielectric layer is deposited to cover the bottom conductive layer yet expose the “tall” top anode electrode. A top conductive layer is then deposited over each dot so a group of diodes is sandwiched between two conductive layers. The diodes in each separate dot are therefore connected in parallel and effectively form a single diode.
Groups of microscopic transistors may be formed in the same way.
More detail of printing microscopic semiconductor components and controlling their orientation on a substrate may be found in Applicant's U.S. Pat. No. 8,852,467, entitled, Method of Manufacturing a Printable Composition of Liquid or Gel Suspension of Diodes, assigned to the present assignee and incorporated herein by reference.
The tiny groups of diodes and/or transistors may be interconnected with a customized conductor pattern to form any type of logic circuit, including very complex circuits. However, if even one diode in a group of parallel-connected diodes has the wrong orientation, the group would not properly act as a rectifier. Therefore, it is important that all diodes electrically connected in parallel have the same orientation. A similar issue may apply to printed transistors, where all transistors electrically connected in parallel in a single group must have the same orientation for the group to act as a single transistor.
Even with the special fluid-dynamic shapes of the diodes and transistors, proper orientation is achieve about 90% of the time. Therefore, on average, one in ten diodes has the wrong orientation. So, the reliability of any complex circuit being formed of interconnected dots of printed diodes or transistors is very low.
Therefore, what is needed is a technique to ensure that all printed diodes electrically connected in parallel have the same orientation. The technique should also be applicable to ensuring that all printed transistors electrically connected in parallel have the same orientation.